Selection of Volume Indicator for the Study of Nasal Drug Absorption

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The nasal absorption of inulin and polyethylene glycol (PEG) 4000, which are not absorbed in the intestinal lumen and are used as volume indicators for intestinal drug absorption experiments, was investigated. No absorption of inulin was detected either by the in situ recirculating perfusion method in the nasal cavity or by the deposit method in the nasal cavity. On the other hand, PEG 4000 showed an absorption ratio of approximately 40 to 50% in the in situ recirculating perfusion method. The absorption ratio of PEG 20000 was approximately equal to that of PEG 4000 but fluorescein isothiocyanatedextran (FITC-dextran, MW 20000) was not absorbed. Such apparent absorption of PEG in the nasal cavity might be due to the interaction between PEG and the nasal membrane, that is, the adsorption of PEG on the nasal membrane, since a higher concentration of PEG 4000 decreased the apparent absorption. The simultaneous perfusion of inulin and PEG 4000 also decreased the apparent absorption of PEG 4000, suggesting a possible interaction between inulin and PEG 4000. Consequently, it was concluded that inulin and FITC-dextran can be used as volume indicators in nasal absorption experiments, but PEG 4000 and PEG 20000 cannot.